Under standardised lighting conditions the affect at the sensor is precisely the same every time you expose it for 1/100th second @ f/8. That is "the exposure"... and it made in accordance with an effective ISO, even if not the ISO the camera happens to be set at... (see below)

The exposure does NOT change because the processing changes. In this regard ISO is just processing.

The sensor readout is not treated the same if the ISO setting is different. So exposing for ISO 200 with the camera set at ISO 400 is simply not the same as exposing at ISO 200.

It doesn't matter what the ISO is at the point of exposure because ISO only determines output afterwards. Output from the exposure is variable depending on how it's processed, and doesn't itself determine the exposure unless you allow it to in reading the meter. As we have seen, you can overexpose or underexpose from the meter, anytime, if you choose to.

But a delivered 1/100th @ f/8 is always 1/100th at f/8, and that will always be the same exposure no matter how it is arrived at...

.... no matter how much underexposure is deliberately applied to nominally "higher" ISO settings, or how much overexposure has been added to nominally "lower" ISO settings. If the resultant exposure is 1/100th @ f/8, and that is what is delivered to the sensor by the shutter and diaphragm working together, then that is always the same, if the light strength is the same.

That is why 400-ISO shot with one stop's worth of overexposure for the sake of ETTR, is identical to 200-ISO shot straight. Please take note: Not just "similar in every way that matters"... but THE SAME, NO DIFFERENCE.

Now, you can fart about with the histogram as much as takes your fancy after the event, but at the point of shooting they are THE SAME, NO DIFFERENCE, photographically identical.

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Regards,Baz="Ahh... But the thing is, these guys were no ORDINARY time travellers!"